Eriolangin is a highly oxygenated sesquiterpene lactone of the rare 1,10-seco-eudes-manolide type, isolated from extracts of Eriophyllum lanatum Forbes (Compositae). The lactone shows significant in vivo activity against P-388 leukemia in mice and in vitro activity against cells derived from human carcinoma of the nasopharynx (KB). Eriolangin contains four chiral centers and seven sites of functionality (carbonyl groups, hydroxy groups, and double bonds) distributed over twenty carbon atoms which are arranged in two rings. Eriolangin thus represents a significant and difficult synthetic challenge both with respect to controlled formation of carbon-carbon double bonds as well as to the selective manipulation of a variety of functional groups. Aromatin is a pseudoguaianolide sesquiterpene lactone isolated from Helenium aromaticum. Pseudoguaianolides represent the largest class of sesquiterpenes known and essentially all of the representatives of this skeletal type exhibit cytotoxic activity. Aromatin is typical of the C15 sesquiterpenes containing five chiral centers and three rings. However, aromatin is a minor representative of the pseudoguaianolides in that it bears the C2 methyl group in the alpha configuration and has, in addition, a cyclopentenone residue instead of the more usual cyclopentanone residue. These two structural features considerably complicate projected syntheses of this material while at the same time making the contemplation of synthesis of aromatin that much more exciting. Although both eriolangin and aromatin are potentially exciting chemotherapeutic agents, they are not available in significant amounts from natural sources and a promising approach to obtaining these materials in quantity would appear to be by total synthesis. Thus we herein propose efficient and stereospecific total syntheses of both eriolangin and aromatin. We intend to submit intermediates leading to eriolangin and aromatin as well as the synthetic natural products themselves to the Cancer Chemotherapy National Service Center as well as the Department of Oncology here at the University of Rochester.